Throttle valve control system for an internal combustion engine

ABSTRACT

A throttle valve control system for a vehicle-mounted internal combustion engine, whereby engine operating parameters relating to engine load are detected, and a target value of a first engine operating parameter is established in accordance with an engine rotational speed, for example a target value which will endure minimum fuel consumption. The throttle valve is driven towards a control opening angle which is determined such as to reduce an amount of deviation of an actual value of the first engine operating parameter from the target value, but is held below an upper limit opening angle which is determined in accordance with an engine operating parameter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a throttle valve control system forcontrolling the opening angle of a throttle valve of an internalcombustion engine.

2. Description of Background Information

A prior art throttle valve control system is described, for example, inJapanese Laid-open Patent No. 60-192843, which describes an apparatuswhereby a throttle valve is driven to an opening angle which isdetermined in accordance with the operating position of the acceleratorand the engine rotational speed, for providing improved engine response.Means have also been envisaged for controlling the throttle valveopening angle such as to reduce the engine fuel consumption, for exampleby deriving a minimum fuel consumption factor in accordance with theengine rotational speed, setting a target value for the pressure withinthe intake pipe of the engine (referred to in the following as theinduction manifold pressure), and driving the throttle valve such as toreduce the amount of deviation between the actual induction manifoldpressure and the target induction manifold pressure. Such a system hasbeen proposed hitherto by the assignees of the present invention.

However with a throttle valve control system whereby the throttle valveis controlled such as to make the actual induction manifold pressurebecome equal to a target inlet manifold pressure, there is a tendencyfor the throttle valve to be driven to an excessively high opening anglewhen the engine is used in a region at a high altitude, i.e. is operatedunder a lower atmospheric pressure than normal. As a result, if thethrottle valve is abruptly controlled such as to move in the closingdirection, there will be a substantial amount of control delay. Thiscontrol delay is introduced as a result of the excessively opencondition of the throttle valve. Thus, satisfactory engine operatingresponse may not be obtained.

Furthermore usually with such a throttle valve control system, the moredeeply the accelerator pedal is depressed, the greater will be theamount of control which is applied to the throttle valve opening angle.However since the range through which the throttle valve can be drivenby such control extends from a condition of being fully closed to thatof being fully opened, a large degree of control overshoot can occurwhen the throttle valve is driven in accordance with the amount ofdeviation between a detected value and a target value. An excessiveamount of throttle valve opening can thereby result, which produces adelay in response to such control and can cause fluctuations in theengine output power. Satisfactory engine operation may therefore not beattainable.

SUMMARY OF THE INVENTION

It is a first objective of the present invention to provide a throttlevalve control system for an internal combustion engine wherebysatisfactory engine operation can be assured at all times.

It is a further objective of the present invention to provide a throttlevalve control system for an internal combustion engine wherebysatisfactory engine operation can be reliably attained when the engineis operated in regions at high altitudes.

It is a further objective of the present invention to provide a throttlevalve control system for an internal combustion engine wherebysatisfactory engine operation can be reliably attained when theaccelerator pedal is depressed by a substantial amount.

In order to achieve the objectives set out above, a throttle valvecontrol system according to the present invention comprises settingmeans for setting a target value of a first engine operating parameter,drive means for driving the throttle valve in accordance with a detectedvalue of the first engine operating parameter such as to reduce adeviation between this detected value and the target value, with thedrive means also functioning to set an upper limit value of the throttlevalve opening angle in accordance with a second engine operatingparameter which is different from the first engine operating parameterand to control the throttle valve opening angle to be held below thisupper limit value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the general configuration ofembodiments of the present invention;

FIG. 2 is a block diagram of a specific configuration for a controlcircuit in the system of FIG. 1;

FIG. 3 is a flow chart for describing the operation of CPU 27 in a firstembodiment of the present invention;

FIG. 4 is a diagram showing a characteristic of a P_(BAref) data mapwhich is stored in a ROM 28 prior to engine operation;

FIG. 5 is a diagram showing a relationship between engine rotationalspeed N_(e) and throttle valve upper limit opening angle θ_(H) which isstored in ROM 28 prior to engine operation;

FIG. 6 shows the characteristic of a Δθ_(th) data map which is stored inROM 28 prior to engine operation;

FIG. 7 is a flow chart of the operation of CPU 27 for a secondembodiment of the present invention;

FIG. 8 is a flow chart of the operation of CPU 27 for a third embodimentof the present invention;

FIG. 9 is a diagram showing a characteristic of a relationship betweenaccelerator pedal angle θ_(ACC) and throttle valve upper limit openingangle θ_(H) ;

FIG. 10 is a flow chart of the operation of CPU 27 for a fourthembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The preferred embodiment of the present invention will be described withreference to the accompanying drawings.

A throttle valve control system mounted in a motor vehicle is shown inFIG. 1 as the preferred embodiment of the present invention. Anaccelerator pedal 1 is coupled to one end of an angle bracket 2 which ismounted by a shaft 3 such as to permit swinging movement of theaccelerator pedal with respect to the floor of a vehicle. A returnspring 4 is coupled to the other end of bracket 2, and urges theaccelerator pedal 1 upwards to an idling position. An acceleratoroperating position sensor 7 consisting of a potentiometer is coupled tothe shaft 3, and produces an output voltage in accordance with theoperating position of the accelerator pedal 1, i.e. in accordance withthe accelerator pedal angle. This angle is defined as the angle throughwhich the shaft 3 has rotated about the axis thereof, from the idlingposition of the accelerator pedal 1.

A throttle valve opening sensor 14 similarly consists of a potentiometerwhich is coupled to a shaft 12a of throttle valve 12, mounted in theengine intake pipe 11, and generates an output voltage in accordancewith the degree of opening of throttle valve 12. The shaft 12a ofthrottle valve 12 is also coupled to the drive shaft of a pulse motor15.

The accelerator operating position sensor 7, the throttle valve openingsensor 14 and the pulse motor 15 are connected to a control circuit 17.Also coupled to the control circuit 17 are a crank angle sensor 18 forgenerating a pulse each time the crankshaft of the engine (not shown inthe drawings) reaches a predetermined angular position during rotationof the crankshaft, an absolute pressure sensor 19 for generating anoutput signal which represents an absolute induction manifold pressure,and an injector 20 which injects fuel into engine cylinders of engine16.

As shown in FIG. 2, the control circuit 17 contains a level convertercircuit 21 which performs level conversion of the respective outputsignals from the accelerator pedal operating position sensor 7, thethrottle valve opening sensor 14, and the absolute pressure sensor 19.The control circuit 17 also includes a multiplexer 22 which receives thelevelconverted output voltage signals from level converter circuit 21and selects one of these output signals to be produced as output, an A/Dconverter 23 which performs analog-digital conversion of the selectedoutput voltage from multiplexer 22, a waveform shaping circuit 24 forperforming waveform shaping of the output signal from the crank anglesensor 18, a counter 25 for measuring the intervals between generationof successive TDC (top dead-center) signals which are produced as pulsesignals by the waveform shaping circuit 24, by counting clock pulsessupplied from a clock pulse generating circuit (not shown), a drivecircuit 26a which drives the pulse motor 15, a drive circuit 26b fordriving the injector 20, a CPU (Central Processing Unit) 27 whichperforms digital operations in accordance with programs, a ROM (ReadonlyMemory) 28 in which programs and data are stored prior to operation ofthe engine, and a RAM (Random Access Memory) 29. The multiplexer 22, theA/D converter 23, the counter 25, the drive circuits 26a and 26b, theCPU 27, the ROM 28 and the RAM 29 are mutually interconnected by a bus30. Although not shown in the drawings, the CPU 27 also receives clockpulses from a clock pulse generating circuit. The CPU 27 functions astarget value setting means, and the CPU 27 and the drive circuit 26afunction in combination as throttle valve drive means.

Respective data for the accelerator pedal angle θ_(ACC), the throttlevalve opening angle θ_(th), and the absolute induction manifold pressureP_(BA), selectively transferred by from the A/D converter 23, togetherwith data representing the engine rotational speed N_(e), are suppliedto the CPU 27 through the bus 30. The CPU 27 executes read-in of therespective data in accordance with a processing program which is storedin ROM 28, in synchronism with the clock pulses. CPU 27 also performsprocessing as described hereinafter for generating pulse motor valveopening drive commands, pulse motor valve closing drive commands, andpulse motor drive halt commands (to halt operation of the pulse motor)which are supplied to the drive circuit 26a to drive the pulse motor 15.

The operation of a throttle valve control system according to a firstembodiment of the present invention will now be described with referenceto the operating flow of CPU 27 which is shown in FIG. 3.

At predetermined periodic intervals, the CPU 27 executes read-in of theengine rotational speed N_(e), the absolute induction manifold pressureP_(BA), and the throttle valve opening angle θ_(th) (step 51), andsearches for a target absolute induction manifold pressure P_(BAref) inaccordance with the engine rotational speed N_(e) which has been read in(step 52). In addition, an upper limit opening angle θ_(H) is searchedfor, based upon the engine rotational speed N_(e) which has been read in(step 53). A P_(BAref) data map of values of target absolute inductionmanifold pressure which provide a minimum fuel consumption coefficient,for respective values of engine rotational speed Ne, is stored in ROM28, and has the characteristic shown in FIG. 4. A θ_(H) data map, ofvalues of throttle valve upper limit opening angle θ_(H) with respect toengine rotational speed N_(e) is also stored in ROM 28, having thecharacteristic shown in FIG. 5. In this way, a target absolute inductionmanifold pressure P_(BAref) can be searched for in the P_(BAref) datamap, in accordance with the engine rotational speed N_(e) which has beenread in, while the upper limit opening angle θ_(H) can be searched forin the θ_(H) data map in accordance with engine rotational speed N_(e).A decision is made as to whether or not the throttle valve opening angleθ_(th) which has been read in is equal to the upper limit opening angleθ_(H) (step 54). If θ_(th) =θ_(H), then a pulse motor drive halt commandis issued (step 55). If θ_(th) ≠θ_(H), then a decision is made as towhether or not the throttle valve opening angle θ_(th) which has beenread in is greater than the upper limit opening angle θ_(H) (step 56).If θ_(th) >θ_(H), then a pulse motor valve closing drive command isissued to the drive circuit 26a, to drive the throttle valve 12 in theclosing direction (step 57). If θ_(th) <θ_(H), then the deviationΔP_(BA) between the target absolute induction manifold pressureP_(BAref) and the absolute induction manifold pressure P_(BA) which hasbeen read in is computed (step 58). An opening angle correction quantityΔθ_(th) of throttle valve 12 is then searched for in a data map ofΔθ_(th) with respect to manifold pressure deviation ΔP_(BA) which isstored beforehand in ROM 28 and has the characteristic shown in FIG. 6(step 59). The opening angle correction quantity Δθ_(th) which is thusobtained is added to the throttle valve opening angle θ_(th) which wasread in, to thereby compute a control opening angle θ_(OUT) (step 60). Adecision is then made as to whether or not the opening angle θ_(th)which was read in is equal to the control opening angle θ_(OUT) (step61). If θ_(th) =θ_(OUT), then a pulse motor drive halt command isgenerated and issued to the drive circuit 26a (step 55). If θ_(th)θ_(OUT), then a decision is made as to whether or not θ_(th) is greaterthan θ_(OUT) (step 62). If θ_(th) >θ_(OUT), then since this indicatesthat the throttle valve opening angle is excessively large with respectto the engine rotational speed, a pulse motor valve-closing drivecommand is issued to drive circuit 26a , whereby the throttle valve isdriven in the closing direction (step 57). If θ.sub. is not found to begreater than θ_(OUT) in step 62, and hence is less than θ_(OUT) , then apulse motor valve-opening drive command is issued to drive circuit 26a ,whereby the throttle valve is driven in the opening direction (step 63).

The drive circuit 26a responds to a pulse motor valve-opening drivecommand by executing rotation by pulse motor 15 in the forward directionto thereby drive the throttle valve 12 towards the valve openingcondition, and responds to a pulse motor valve-closing drive command byexecuting rotation by pulse motor 15 in the reverse direction to therebydrive the throttle valve 12 towards the closed condition. Drive circuit26a moreover responds to a pulse motor drive halt command by halting therotation of pulse motor 15, to thereby maintain the current degree ofthrottle valve opening. In this way the throttle valve opening angleθ.sub. is controlled such as to follow the control opening angleθ_(OUT). In addition, if the control opening angle θ_(OUT) should exceedthe upper limit opening angle θ_(H), control is executed such that thethrottle valve opening angle θ_(th) is held below this upper limitθ_(H).

With the first embodiment of the present invention described above, ifθ_(th) is less than θ_(H), the system operates such as to reduce thedeviation between the target absolute induction manifold pressure (whichprovides minimum fuel consumption at the current speed of enginerotation) and the actual value of absolute induction manifold pressure.A second embodiment of a throttle valve control system according to thepresent invention will now be described, with reference to the flowchart of FIG. 7. With the second embodiment, a target opening angleθ_(thref) which provides minimum fuel consumption at the current enginerotation speed is obtained by searching a data map that has beenpreviously stored (step 52a). If θ_(th) <θ_(H), then a decision is madeas to whether or not θth.sub. is equal to θ_(thref) (step 61a). If theyare not found to be equal, then a decision is made as to whether or notthe throttle valve opening angle θ_(th) is greater than θ_(thref) (step62a).

It should be noted that it would be equally possible to arrange that ifthe control opening angle θ_(OUT) (obtained by computation in step 60)is greater than the upper limit opening angle θ_(H), then the throttlevalve is driven to an angle of opening which is equal to the upper limitopening angle θ_(H).

Thus as described above, with a throttle valve control system for aninternal combustion engine according to the first or second embodimentof the present invention, a throttle valve is controlled such as to beheld below an upper limit opening angle which is determined inaccordance with the engine rotational speed. As a result, when theengine is operated in a region at high altitude, excessive opening ofthe throttle valve is prevented. In this way, if the throttle valve isactuated such as to be rapidly moved in the opening direction, thethrottle valve control system acts to prevent any unnecessary delaybefore the engine attains the required output power level. Enhancedoperating response is thereby obtained.

A third embodiment of the present invention will now be described,referring to the flow chart of FIG. 8.

In FIG. 8, the CPU 27 executes read-in of the engine rotational speedN_(e) , the absolute induction manifold pressure P_(BA) , the throttlevalve opening angle θ_(th) , and the accelerator pedal angle θ_(ACC), atpredetermined periodic intervals (step 511), and searches for a targetabsolute induction manifold pressure P_(BAref) in accordance with theengine rotational speed N_(e) which has been read in (step 52). Inaddition, an upper limit opening angle θ_(H) is searched for, based uponthe accelerator pedal angle θ_(ACC) which has been read in (step 512). AP_(BAref) data map of values of target absolute induction manifoldpressure which provide a minimum fuel consumption coefficient, forrespective values of engine rotational speed N_(e), is stored beforehandin ROM 28, and has the characteristic shown in FIG. 4. A θ_(H) data map,of values of throttle valve upper limit opening angle θ_(H) with respectto accelerator pedal angle θ_(ACC) is also stored in ROM 28, having thecharacteristic shown in FIG. 9. In steps 52 and 512 respectively, thetarget absolute induction manifold pressure P_(BAref) is searched for inthe P_(BAref) data map, in accordance with the engine rotational speedN_(e) which has been read in, while the upper limit opening angle θ_(H)is searched for in the θ_(H) data map in accordance with the acceleratorpedal angle θ_(ACC) which has been read in. A decision is made as towhether or not the throttle valve opening angle θ_(th) which has beenread in is equal to the upper limit opening angle θ_(H) (step 54). Ifθ_(th) =θ_(H), then a pulse motor drive halt command is issued (step55). If θ_(th) ≠θ_(H), then a decision is made as to whether or not thethrottle valve opening angle θ_(th) which has been read in is greaterthan the upper limit opening angle θ_(H) (step 56). If θ_(th) >θ_(H),then since this indicates that the throttle valve opening angle isexcessively large, with regard to the engine rotational speed, a pulsemotor valve closing drive command is issued to the drive circuit 26a ,to drive the throttle valve 12 in the closing direction (step 57). Ifθ_(th) <θ_(H), then the deviation ΔP_(BA) between the target absoluteinduction manifold pressure P_(BAref) and the absolute inductionmanifold pressure P_(BA) which has been read in is computed (step 58),and an opening angle correction quantity Δθ_(th) of throttle valve 12 isthen obtained by searching a Δθ.sub. data map which is stored beforehandin ROM 28 and has the characteristic shown in FIG. 6 (step 59). Theopening angle correction quantity Δθ_(th) which is thus obtained isadded to the throttle valve opening angle θ.sub. which was read in, tothereby compute a control opening angle θ_(OUT) (step 60). A decision isthen made as to whether or not the opening angle θ_(th) which was readin is equal to the control opening angle θ_(OUT) (step 61). If θ_(th)=θ_(OUT), then a pulse motor drive halt command is generated and issuedto the drive circuit 26a (step 55). If θ_(th) ≠θ_(OUT) , then a decisionis made as to whether or not θ_(th) is greater than θ_(OUT) (step 62).If θ_(th) >θ_(OUT), then a pulse motor valve-closing drive command isissued to drive circuit 26a , whereby the throttle valve is driven inthe closing direction (step 57). If θ_(th) is not found to be greaterthan θ_(OUT) in step 62, and hence is less than θ_(OUT), then a pulsemotor valve-opening drive command is issued to drive circuit 26a,whereby the throttle valve is driven in the opening direction (step 63).

The drive circuit 26a responds to a pulse motor valve-opening drivecommand by executing rotation by pulse motor 15 in the forward directionto thereby drive the throttle valve 12 towards the valve openingcondition, and responds to a pulse motor valve-closing drive command byexecuting rotation by pulse motor 15 in the reverse direction to therebydrive the throttle valve 12 towards the closed condition. Drive circuit26a moreover responds to a pulse motor drive halt command by halting therotation of pulse motor 15, to thereby maintain the current degree ofthrottle valve opening. In this way the throttle valve opening angleθ_(th) is controlled such as to follow the control opening angleθ_(OUT). In addition, if the control opening angle θ_(OUT) should exceedthe upper limit opening angle θ_(H), control is executed such that thethrottle valve opening angle θ_(th) is held below this upper limitθ_(H).

With the third embodiment of the present invention described above, ifθ_(th) is less than θ_(H), the system operates such as to reduce thedeviation between the target absolute induction manifold pressure (whichprovides minimum fuel consumption at the current speed of enginerotation) and the actual value of absolute induction manifold pressure.A fourth embodiment of a throttle valve control system according to thepresent invention will now be described, with reference to the flowchart of FIG. 10. With the fourth embodiment, a target opening angleθ_(thref) which provides minimum fuel consumption at the current enginerotation speed is obtained by searching a data map that has beenpreviously stored (step 52a). If θ_(th) <_(H), then a decision is madeas to whether or not θ_(th) is equal to θ_(thref) (step 61a). If theyare not found to be equal, then a decision is made as to whether or notthe throttle valve opening angle θ_(th) is greater than θ_(thref) (step62a), and control of the pulse motor is executed in accordance with theresult of the decisions made in steps 61a and 62a. It should be notedthat it would be equally possible to arrange that if the control openingangle θ_(OUT) (computed in step 60) is greater than the upper limitopening angle θ_(H), then the throttle valve is driven to an angle ofopening which is equal to the upper limit opening angle θ_(H) withoutdetecting whether the actual throttle valve opening angle θ_(th) isgreater than the upper limit opening angle.

Furthermore, although in the third and fourth embodiments of the presentinvention described above the throttle valve 12 is directly driven by apulse motor 15, the present invention is equally applicable to anapparatus whereby the operation of the throttle valve is linked toactuation of the accelerator pedal, and whereby a stopper is used tolimit the degree of opening of the throttle valve, with the position ofthe stopper being varied by drive applied from a motor, e.g. a pulsemotor.

With the third and fourth embodiments of the present invention for aninternal combustion engine according to the present invention asdescribed hereinabove, since the throttle valve is driven such that theopening angle is held below an upper limit opening angle, which isdetermined in accordance with the operating position of the acceleratorpedal, overshoot resulting from excessive opening of the throttle valveis prevented. Thus, fluctuations in the engine output power can beprevented, and enhanced engine response can be attained.

With each of the first through fourth embodiments of the presentinvention described hereinabove, an opening angle correction quantityΔθ_(th) is obtained by using a Δθ_(th) data map. However it would beequally possible to obtain this opening angle correction quantity byexecuting the computation Δθ_(th) =k_(l) ·ΔP_(BA), or Δθ_(th) =k₂ ·N_(e)·ΔP_(BA) (where k₁ and k₂ are constants.)

Moreover with the respective embodiments of the present inventiondescribed above, when a pulse motor valve opening drive command or apulse motor valve closing drive command is issued from CPU 27, the drivecircuit 26a responds by generating pulses to be supplied to the pulsemotor 15 which are produced at a fixed frequency. However it would beequally possible to arrange that the CPU 27 issues to the drive circuit26a a pulse motor valve opening drive command or a pulse motor valveclosing drive command which expresses a number of pulses correspondingto the difference between the actual throttle valve opening angle θ_(th)and the control opening angle θ_(OUT), or the difference between θ_(th)and the upper limit opening angle θ_(H). In this case, the drive circuit26a will supply only the designated number of drive pulses to pulsemotor 15.

Furthermore it should be noted that a throttle valve control systemaccording to the present invention is applicable to use together with aCVT (automatic transmission) system, etc, which controls the enginerotational speed in accordance with the accelerator pedal operatingposition.

What is claimed is:
 1. A throttle valve control system for controllingan opening angle of a throttle valve disposed in an intake system of aninternal combustion engine which is mounted in a vehicle, the controlbeing executed in accordance with engine operating parameters,comprising:detecting means for detecting a first engine operatingparameter; setting means for setting a target value of said first engineoperating parameter and; drive means for driving said throttle valvesuch as to reduce a deviation between said detected value of said firstengine operating parameter and said target value; said drive meansfurther acting to set an upper limit opening angle of said throttlevalve in accordance with a second engine operating parameter which isdifferent from said first engine operating parameter, and to limit saidthrottle valve opening angle to a value which is lower than said upperlimit opening angle.
 2. A throttle valve control system according toclaim 1, in which said first engine operating parameter is an inductionmanifold pressure, measured at a point in said intake system which isdownstream of said throttle valve.
 3. A throttle valve control systemaccording to claim 1, in which said first engine operating parameter isan opening angle of said throttle valve.
 4. A throttle valve controlsystem according to claim 1, in which said second engine operatingparameter is an engine rotational speed of said internal combustionengine.
 5. A throttle valve control system according to claim 1, inwhich said second engine operating parameter is an accelerator pedalangle which expresses an operating position of said accelerator pedal.6. A throttle valve control system according to claim 1, in which saidsetting means sets a target value of said first engine operatingparameter in accordance with a third engine operating parameter.
 7. Athrottle valve control system according to claim 6, in which said thirdengine operating parameter is an engine rotational speed of saidinternal combustion engine.
 8. A throttle valve control system accordingto claim 7, in which said setting means sets said target value of saidfirst engine operating parameter so as to obtain a minimum fuelconsumption.